Curbs, Wheel Stops and Bollards

The last two yards off a truck at a fuel canopy job went into eight bollard footings. Nobody sampled that concrete; the specification only called out testing for the slab. What I did write down was the six gallons the driver added at the tail end, because recording it is the part of the job that belongs to me. Fourteen months later a delivery truck clipped bollard number three and it leaned. They cored the footing: 2,140 psi against a 3,000 psi design.

I run field tests and I have no say in how any of it gets built. What I can tell you is which of these three gets built to a number and which gets built by eye.

Three items, three different jobs

Curbs direct water and mark an edge. A 6 inch barrier curb standing 6 inches proud stops a car creeping at 3 mph. It was never meant to stop anything heavier.
Wheel stops tell a driver where to quit. They are a parking aid, not a barrier. A pickup with 18 inches of front overhang still reaches the wall behind one, so they get set 24 to 30 inches off whatever is being protected.
Bollards are the only one of the three meant to absorb an impact, and only when the footing was built for it. Low-speed impact performance is covered by ASTM’s vehicle barrier test methods. A pipe dropped in a posthole is not rated for anything.

What actually gets measured

On curb and gutter work the spec I test against is usually 4,000 psi with 5 to 7 percent entrained air anywhere that freezes, at a slump near 2 inches for machine-extruded curb or 3 to 4 inches hand-formed. Air is the number I watch hardest: curb carries a lot of exposed surface for its volume, it catches the plow blade, and it scales before anything else on the lot.

Sampling has rules that feel pedantic until a result gets argued about. A composite field sample comes out of the middle of the load, after the first 10 percent has discharged and before the last 10 percent. Tail-end concrete — the kind that fills bollard footings and curb returns — almost never has a cylinder behind it.

Footings are where it goes wrong

A standard non-rated bollard is 4 to 6 inch schedule 40 pipe, embedded 36 to 48 inches in a footing 12 to 18 inches across, filled with concrete afterward. Depth matters more than diameter. What I get sent to core is almost never a broken pipe — the assembly rotates in soft backfill because the hole went 24 inches deep instead of 42. An impact drives a concentrated load into a small patch of soil, the same arithmetic as point loads from jacks, stands and dumpster wheels.

Spacing runs 4 to 5 feet on center. Wider than that and a vehicle fits between two of them.

What each one costs

Extruded curb: $9 to $18 per linear foot on a long open run.
Formed cast-in-place curb, 6 by 18 inches: $22 to $40 per linear foot, higher on short-radius work.
Precast wheel stop, 6 feet: $45 to $110 installed, pinned with two lengths of #4 rebar.
Rubber or recycled plastic wheel stop: $60 to $130. Will not spall, but walks off.
Concrete-filled pipe bollard: $350 to $900 each, most of it excavation and concrete rather than pipe.
Crash-rated bollard on an engineered foundation: $2,500 to $7,000 each. A different product, not an upgrade.

Frequently asked questions

How deep does a bollard footing need to be? For an ordinary protective bollard, 36 to 48 inches of embedment in a 12 to 18 inch footing, and below the local frost depth, which runs near 30 inches across much of the Mountain West. Depth is what resists rotation. Adding diameter to a shallow hole buys very little.

Do wheel stops have to be anchored? Yes, if you want them to stay put. Precast stops take two pins, #4 rebar or 1/2 inch anchors driven 10 to 12 inches into the pavement. Unpinned, they get shoved out of line within a season.

Why does the same stretch of curb break up every year? Usually low air content plus de-icer. Air-entrained concrete needs 5 to 7 percent measured in the field, not on the mix design sheet, and air is lost to pumping, over-vibration and long haul times. When a curb scales and the slab beside it does not, the air test on that load is the first thing worth looking up.

Pavement guidance: American Concrete Pavement Association.